accepted, as I think it must be, lies in the proof which it furnishes
that there cannot possibly be an undiscovered oasis anywhere near a
point seven or eight days from Dakhla in the direction of Kufra. A
consideration of the static water-levels and the contours of the ground
would lead us to this conclusion if the views I have advanced on the
underground-water question are correct; but the fact that the raiders
would never have made such a large water-dump if water could have been
readily got from a well in the vicinity makes the conclusion almost
certain independently of my hypothesis, and thus incidentally tends to
support the latter. Is it possible that “Zerzura,” which I am told
signifies in Arabic a starling (but is commonly applied to any small
bird), is here a corruption of some other name derived from “zeer,” a
water-jar, and that instead of “the _oasis_ of the blacks,” Zerzura was
really “the _water-depôt_ of the blacks”?
Schweinfurth has recorded[31] a story which was told him in Kharga
Oasis, that in 1872 some Arabs of a Darfur caravan, who had missed the
road, found a small oasis about 1½ days’ journey to the west of Beris.
The oasis was said to contain pools full of wild geese, date-palms, and
a temple. People who went out of Beris to find the place returned
unsuccessful. I am, however, rather inclined to think that the story has
some basis of fact, because in 1898 I myself found springs and traces of
ancient conduits in the dunes north-west of Beris, and there may be
other water-sources beyond the point which I reached.[32]
A writer in the ninth edition of Murray’s ‘Guide to Egypt,’ published in
1896, gives the following different statements of Arabs as to the
position of Zerzura:
(1) Some days south of the Dakhla Oasis.
(2) Five days west of Farafra Oasis.
(3) Three days west of Dakhla Oasis.
(4) Two or three days west of Selima Oasis.
The first of these statements would correspond sufficiently well with
Bir Terfawi, which is about 280 kilometres due south of Dakhla Oasis;
the second would place Zerzura about in latitude 27°, longitude 26°; the
third corresponds with the second account given to Wilkinson; while the
fourth would place it far to the south-west, in latitude 21½°, longitude
28°, or rather less than halfway between Bir Terfawi and Merga.
Mr. Harding King, who in his journeys in the Libyan Desert in 1909 and
1911 devoted much attention to the collecting of native information
regarding its geography, thinks that “Zerzura” may possibly be only a
generic name applied to any mythical or undiscovered oasis.[33] He heard
the name applied to the following localities:
(1) Rohlfs’ “Sersura.”
(2) The “Egyptian Oasis,” said to have been seen by an Arab from the top
of a high black hill lying in the dune-belt ten long days by ordinary
caravan from Kharga. Another Arab is said to have seen what is possibly
the same place eight days somewhere to the south of Dakhla. Both these
accounts agree that the place is a large oasis lying at the foot of a
scarp and containing olive trees.
(3) A stone temple eighteen hours’ journey west of Gedida in Dakhla
Oasis.
The information given to Mr. Harding King as to the position of the
“Egyptian Oasis” would place it about in latitude 23°, longitude 28½°,
or only some 50 kilometres north-west of Bir Terfawi; in fact,
considering the vagueness of the information, it might correspond fairly
well with Terfawi itself, except that there are no olive trees at
Terfawi, nor is that place overlooked by any escarpment or hill. The
“high black hill in the dune-belt” may just possibly be one of those I
mapped near the farthest point I reached with Moore in 1916, in about
latitude 24°, longitude 26°, though this would imply a direction south-
west of Dakhla, not south. It is not likely to be Gebel Kamil, as that
mountain lies much nearer to Merga than to Dakhla.
The “stone temple,” according to the information given to Mr. Harding
King, would be about 80 kilometres west of Dakhla Oasis, in about
latitude 25½°, longitude 28°, or not very far from the second of the
positions indicated by Wilkinson for Zerzura. But I think it is likely
that the statement really refers to the “Deir el Hagar,” a well-known
temple ruin much nearer to Dakhla.
So much for the various statements as to whereabouts Zerzura _may be_.
Let us now inquire where it is _not_. On the map I have indicated the
principal routes followed by explorers of the southern and western parts
of the Libyan Desert during the last fifty years. We may be tolerably
certain that Zerzura is not on, or very close to, any of these routes;
for although a depression within a kilometre or so of one’s track may
easily be passed without notice, the existence of a large oasis, such as
most of the traditions make Zerzura out to be, would almost certainly be
betrayed to an explorer by animal-tracks leading to it from considerable
distances, except possibly in places where the ground was very sandy.
[Illustration: _Pottery Hill from the south: at foot, petrol and water
supplies of Prince Kemal el Din’s Expedition of 1923_]
[Illustration: _Jars at northern foot of Pottery Hill found by Prince
Kemal el Din in 1923_]
[Illustration: _Jars, worn away by sand-laden winds, found by Dr. Ball
in 1917 at southern foot of Pottery Hill_]
There is another method now available to us by which we may narrow down
the search for Zerzura or other “lost” oases; and that is, by a
consideration of the general contours of the country and those of the
static water-surface. Every oasis in the Libyan Desert must owe its
existence to one or other of two conditions: either it must depend on
springs fed by local rainfall, in which case, like the oases of Owenat
and Arkenu, it probably lies near to mountains of considerable height;
or else it must depend on underground supplies, and must therefore lie
in a depression wherein the ground-level and static water-level are
practically coincident, as in the cases of Kharga, Dakhla, Farafra,
Baharia, and Siwa. It is highly doubtful whether any mountain masses at
all approaching the altitude of Arkenu and Owenat can remain
undiscovered in any of the various areas in which Zerzura has been
traditionally placed. Zerzura is immensely more likely to be in a
depression, and indeed Wilkinson’s name _Wadi_ Zerzura almost
conclusively points to that view. The depression is more likely to be
shallow than very deep, for it presumably lies in the sandstone country
of the south-west, and all the known depressions of great depth are
confined to the limestone country of the north-east. It is quite easy to
trace out on our new map the areas wherein the static water-surface
would be reached by a depression of say 50 or 100 metres below the
general ground-level as indicated by the contours. We must, however,
remember that our ground-contours are liable to be considerably in error
in areas where observations have been few—that is, in precisely those
areas where the depression, if it exists, is most likely to be found. So
we must allow a good margin for our depth, and I have chosen 100 metres
on this account. On the map I have drawn the “locus” of points in the
southern part of the Libyan Desert where the static water-surface is 100
metres lower than the general ground-surface[34]; and I have edged with
red the only areas in the west and south in which the two surfaces are
within 100 metres of each other—that is to say, the areas within which
comparatively shallow depressions with underground springs _must_ lie,
if our contours of the two surfaces are drawn with even approximate
correctness. It will be seen from the map that this restricts the search
very considerably. In fact, if Zerzura is within the frontiers of Egypt,
it lies in all probability either to the west of longitude 26° 20′ and
north of latitude 26°, or to the east of longitude 27° and south of
latitude 23° 30′. We may dismiss from our field of search all the broad
tract of rising ground which extends from near the Dakhla escarpment
south-westwards towards Owenat; for unless Zerzura is in a depression of
great depth, it cannot possibly lie within this tract. This
consideration shows that most of the previous rough estimations of the
possible position of Zerzura must have been erroneous; and indeed it is
remarkable how few of the various explorers’ tracks traverse the only
two areas within which Zerzura, if it exists, almost certainly lies. The
northern area has only been crossed by the Rohlfs expedition of 1874,
and that near its eastern edge; while the western part of the southern
area has only been crossed by Prince Kemal el Din’s expedition of 1925.
Of all the Arab traditions, only those which would place Zerzura far to
the west of Farafra, or far to the south-south-west of Dakhla, can now
have any high degree of credibility. It can hardly, I think, be doubted
that the various traditions refer to more than one place; and in view of
the almost totally unexplored state of the only two areas in which our
new contour-maps indicate the possibility of unknown oases existing, it
is quite conceivable that at least one oasis may lie within each of
them. In the northern area, Siwa would probably make the best starting-
point from which to conduct a search, as it is easily reached by motor-
car from Alexandria or Cairo, and exploratory journeys southwards from
Siwa would mostly lie along the direction of the dune axes. In the
southern area, Terfawi or Sheb would form the best base for exploration;
at each of these places there is a good water-supply. I am inclined to
think that the southern area is more likely to yield results than the
northern one. Water was found to exist at a point some 15 kilometres
west of Terfawi, and though no other source was observed on the way to
Owenat, it was impossible to see very far on either side of the track,
so that such a source might have been passed within a few miles without
notice. Terfawi itself is very difficult to find, being inconspicuous
even when one is fairly close to it; and as it is in a sandy area,
tracks leading to it are soon obliterated. Another factor which favours
this southern area is that, the country being all Nubian sandstone, the
depth from the surface to the actual water-bearing beds (as
distinguished from the depth to the static water-surface) is certain to
be much less than in the northern area, where Cretaceous strata may
overlie the sandstone; hence there is more likelihood of the existence
of natural springs in the south than in the north.
9. _Can Travel in the Great Tracts of the Libyan Desert which are now
Waterless be facilitated by the Sinking of New Wells?_
It has sometimes been asked whether tracts which it is now difficult or
impossible to cross by camel, owing to the non-existence of wells or
natural springs within them, might possibly be opened up to transport by
the sinking of new wells along a proposed route, as has in fact been
done by the Senussi in the case of the well at Sarra, between Wanianga
and Kufra. Hitherto there have been no data from which to form an
opinion on this question; but a study of the new map will enable at
least a qualified answer to be given.
To be a practicable proposition, a new well must fulfil two conditions:
the first, that the boring must not be required to descend to a very
great depth; and the second, that the water when struck must rise in the
bore to within a reasonable distance, say 20 to 30 metres, of the
ground-level at the place. The first of these conditions will be
satisfied if the geological horizon of the water-bearing bed is
comparatively near the surface; the second, if the level of the static
water-surface in the locality is within 20 or 30 metres of the ground-
level.
As regards the first of these conditions, we know that the water-bearing
beds underlying the Libyan Desert are situated within the geological
formation called the Nubian sandstone. We may therefore eliminate from
our consideration all tracts in which this formation is overlain by any
great thickness of younger rocks, for all these rocks will have to be
passed through in order to tap the water-bearing strata.
Concerning the second condition, our map at once informs us that the
areas in which the static water-surface is within 20 or 30 metres’ depth
below the ground-level are decidedly limited. Even if we suppose that
there may be unknown depressions extending to a depth of 70 metres below
the general level of the country indicated by the contour-lines, we see
that the localities in which the second condition would be fulfilled are
confined to the tracts edged with red on the map. Outside these tracts,
not only have we no chance of discovering oasis-depressions, but we also
have no prospect of being able to bore wells in which water would rise
to within a reasonable distance of the ground-level. Thus the broad
tract of rising ground which extends south-westwards from Dakhla to
Owenat must always remain a waterless waste.
In the Egyptian portion of the Libyan Desert there are, as will be seen
from the map, only two areas in the west and south in which new wells
might successfully be bored: one extending for some 300 kilometres or so
to the south of Siwa Oasis in the neighbourhood of the western frontier,
the other extending for some 400 kilometres westward from the Nile in
the neighbourhood of the southern boundary. Fortunately, however, these
areas are so situated that wells sunk within them might be of
considerable use in opening up the outermost parts of Egypt to
exploration. A well near the western frontier about on the parallel of
26°, for instance, might make it just possible for cars or camels to
reach Owenat directly from Siwa, since it would divide the present
waterless stretch of 830 kilometres into two stretches of about half
that length; while one or two wells near the southern frontier between
the meridians of 27° and 28° would render Owenat fairly accessible to
camels coming from the Nile _viâ_ Terfawi or Sheb, and might be of great
use to explorers or geologists desirous of making a detailed
investigation of the Owenat and Arkenu region. From the little I saw of
Gebel Owenat during my visit to it in 1925, its geology must be of
extreme interest. The south-western part of the mountain appears to be
entirely composed of granite and other crystalline rocks, while the
eastern part presents huge cliffs of sandstone, with crystalline rocks
showing only at the foot; there is evidently a great fault traversing
the mountain mass, with a downthrow to the east; and the thickness of
Nubian sandstone exposed on the eastern precipices is greater than that
at any other place I have seen.[35] Gebel Kissu probably resembles the
south-western part of Owenat in being entirely composed of crystalline
rocks.[36] East of Gebel Owenat there are many igneous hills, some of
which exhibit bands of a dark brown colour. These bands, though probably
mostly igneous dykes, may possibly in some cases be the gozzany outcrops
of veins containing metallic minerals; I had no opportunity of examining
them at close quarters, but I saw enough to make me long for facilities
to undertake such an examination.
It may be remarked that a well in the northern area would probably have
to be very deep, owing to the comparatively high geological horizon of
the surface rocks there; but in the southern area, where the Nubian
sandstone forms the surface rock, no great depth of boring would be
likely to be required in order to tap the water-bearing beds.
Apart from the question of new wells in the more remote parts of the
Libyan Desert, a study of the map gives us some hints which may be of
value should it ever be desired to sink wells in places nearer to the
oases and to the well-known tracks. There appears, for instance, to be
no reason why wells should not be successfully bored at intervals along
the Darb el Arbain between the south end of Kharga and Lagia, or on the
south side of the Qattara and other depressions of the northern part of
the desert. In the southern area, the best sites to select for wells
will be depressions wherein the ground-level approximates most closely
to the static water-level; and readings of an aneroid barometer,
compared with corresponding readings at a place of known altitude, such
as Sheb or Terfawi, would enable the most favourable sites to be
determined. Observations of the geological structure will also be of
importance; for anticlinal folds, by bringing the water-bearing strata
nearer to the surface, would diminish the depth to which borings would
have to be carried to tap the beds; while faulting might likewise
introduce favourable conditions by producing cracks and fissures along
which the water could rise. It may be remarked that tamarisk-bushes are
generally a sign that water exists at no great depth. In regard to wells
in or near the northern depressions, it is obvious that sites on the
south side of the lakes and salt-marshes should be selected; for not
only is the artesian static level higher in the south, but the water is
less likely to be contaminated by salts derived from the lake and
marshes.
10. _The “Tortoise Marshes” of Ptolemy._
The passage in Ptolemy’s ‘Geographia’ (lib. IV. cap. 6, sect. 4) in
which the position of the “Tortoise Marshes” is given may be translated
as follows[37]:
There are two great rivers running into the Mediterranean; one of them
is the Gir, joining Mount Usargala with the Garamantic narrows, from
which, changing its course, the river is located in long. 42°, lat.
16°, and makes the Tortoise Marshes (Chelonitides Paludes), whose
position is long. 49°, lat. 20°.
The information on which Ptolemy based this statement, at least as
regards the river _Gir_, must have been very fragmentary, if not,
indeed, grossly erroneous; for there is no river flowing to the
Mediterranean anywhere near the positions he gives. But there can be
little doubt that his names _Gir_ and _Chelonitides Paludes_ refer to
real places, and there has been much speculation among geographers as to
their identification.
Thus, for instance, Knoetel[38] suggested that the _Gir_ may have been
the Wadi Djedi, to the south of Biskra, and the Tortoise Marshes the
modern Lake Melghir (lat. 34°, long. 6°)[39] Dr. William Smith[40]
thought that the _Gir_ was really a branch of the Niger, and the marshes
the modern Lake Fittri (lat. 13°, long. 18°). On the map of Africa on
the 2-million scale published by the Geographical Service of the French
Army in 1899 the Tortoise Marshes are depicted as lying in about
latitude 19° 20′, longitude 27°, with a note stating that this
delineation is taken from an earlier map of the Nile Basin by Miani, who
regarded the marshes as being connected with the “dry river” which was
then supposed to run northwards through Dakhla Oasis. Colonel Tilho has
lately suggested[41] the lowlands to the north-east of Lake Chad (lat.
18°, long. 17°) as a possible site for the marshes; while still more
recently Mr. Harding King[42] has thought that they might perhaps be
identified with the salt lake of Merga (lat. 19° 3′, long. 26° 19′).
Of the various localities which have been suggested as possible sites
for the Tortoise Marshes, the only one which I have visited is Merga. I
found the salt lake at that place to be very small, covering only some
10 acres; it lies at an altitude of 509 metres above sea-level, and
though it is situated in a rather wide shallow depression, I saw no
traces of any extensive salt-marshes around the lake, while the
configuration of the surrounding country appeared to me to be such that
the depression cannot possibly have formed part of a continuous
drainage-channel.
I do not know whether it has hitherto been suggested that Kufra Oasis
may be the site of the Tortoise Marshes; but on correcting Ptolemy’s
figures for the errors in his adopted position for Alexandria and in the
length which he assumed for a degree of latitude, I find Kufra is in
very much closer agreement with them than any of the places named above.
In Ptolemy’s day, even the latitudes of but few places had been
astronomically observed (Alexandria, where he himself resided, was
supposed by Ptolemy to be in latitude 31°, instead of its true 32° 12′),
and as the only method at that time known for astronomically determining
differences of longitude was by the observation of eclipses, the number
of observed longitudes was smaller still. The process by which Ptolemy
deduced his position for the Tortoise Marshes and other places in the
interior of Libya was most probably that of first estimating their
distances south and west of Alexandria from travellers’ itineraries,
then converting these distances into degrees of latitude and longitude,
and finally subtracting the differences thus found from the latitude and
longitude of Alexandria. But Ptolemy made the great mistake of assuming
the length of a degree of latitude (or of equatorial longitude) to be
500 stades, instead of the 700 stades which it really is. Thus all his
dead-reckonings resulted in differences of latitude and longitude which
were too great in the proportion of seven to five. If we correct
Ptolemy’s position for Alexandria, and his dead-reckoning for the
erroneous assumption which he made regarding the size of the Earth, as
follows:
_Latitude._ _Longitude._
Ptolemy’s position for Alexandria 31° 60° 30′
Ptolemy’s position for the Tortoise
Marshes 20° 49°
------- -------
Ptolemy’s difference of lat. and long. 11° 11° 30′
These differences reduced in the
proportion of 5 to 7 become, in true
degrees and minutes 7° 52′ 8° 12′
The true position of Alexandria is 32° 12′ 29° 53′
------- -------
Whence the corrected position for the
marshes in our modern system becomes 24° 20′ 21° 41′
we get lat. 24° 20′ and long. 21° 41′ for the Tortoise Marshes.
Comparing this position with that of Kufra, we find that the latitude
agrees very closely with the 24° 14′ which Hassanein observed at Taj,
the principal village of that oasis; while the longitude, though more
than a degree and a half west of that of the principal village, is
almost exactly correct for Taiserbo, the north-western oasis of the
Kufra group.
Besides this remarkably close agreement as regards position, Kufra
presents several natural features which would tend to support the view
that it may be the locality which Ptolemy meant by the “Tortoise
Marshes.” Not only is Kufra an extensive tract of relatively low-lying
ground with numerous lakes and salt-marshes of very considerable size,
but it has distinctly the form of a valley. Hassanein Bey repeatedly
refers to it as a valley in his description[43]; Mrs. Forbes also speaks
of the “Wadi of Kufra,” and mentions that as a result of a ride westward
from Taj the “wadi” was found to have no definite ending to the
west.[44] What more natural, therefore, than that some ancient traveller
should have imagined that Kufra was a series of marshes formed by a
river coming from the south-west? And is it not possible that Ptolemy,
in endeavouring to piece together the scraps of information he could
get, may have mistakenly inferred that this river ultimately reached the
Mediterranean, and also have confused the account of it with those of
other streams further south, which may have been branches of the Niger?
11. _The Sand-Dunes._
The sand-dunes of the Libyan Desert have been the subject of careful
studies by Mr. Beadnell and Mr. Harding King, and practically all that
was known concerning them up to the outbreak of the Great War is
contained in the excellent papers by them which were read and discussed
at meetings of the Royal Geographical Society in 1910, 1916, and
1918.[45]